The present invention relates to a device for regulating rotary speed of an alternating current motor having an armature coil connected as a branch of a bridge circuit balanced for a fixed rotary speed and a fixed operational voltage of the motor, and the device further including an adjuster controlled by voltage across a diagonal of the bridge circuit to adjust current flowing through the armature coil.
In an electronic regulation of a universal motor an internal electrical regulating signal is derived from the torque which in turn is derived from the rotary speed or from the current of the motor. The regulating magnitude controls motor voltage or current via an excitation circuit and a power semiconductor. The manner in which the internal regulating magnitude depends on the rotary speed or on torque as well as how the former is processed and manipulated by the excitation circuit determines the behavior of the electric motor in its working range or working point of its characteristic line. From the German publication DE-AS No. 23 12 127, for example, an electric rotary speed regulator is known in which the regulating magnitude is generated by a bridge circuit. The armature coil of the motor and a current measuring resistor is arranged in one branch of the bridge whereas in another of the latter two reference resistors are arranged. The bridge is designed such to as to be balanced at a fixed, average torque of the motor. In the case of loading the motor above this average torque or unloading below the latter the bridge becomes unbalanced. By suitably dimensioning the bridge circuit a fixed course of characteristic lines can be obtained. This prior art arrangement however does not enable to adjust the characteristic lines of individual parameters of the motor.